1. Field of the Invention
The present invention generally relates to a method and apparatus for retransmitting data in a broadband wireless communication system, and in particular, the present invention relates to a method and apparatus for retransmitting data in a multi-hop communication system in which data is transmitted via a Relay Station (RS).
2. Description of the Related Art
The need for a communication system that efficiently provides Internet service has become pressing along with today's development of the communication industry and ever increasing user demands for Internet service. As legacy communication networks were designed mainly for voice service, they suffer from relatively narrow transmission bandwidths and high use cost. To overcome this problem, Orthogonal Frequency Division Multiplexing (OFDM) is under active study as a promising broadband transmission technology.
OFDM is a special case of multi-carrier modulation in which a plurality of orthogonal subcarriers are overlapped with one another. In OFDM, an input serial symbol sequence is converted to parallel symbol sequences and modulated to orthogonal subcarriers, prior to transmission. OFDM finds its various applications in digital transmission technology including Digital Audio Broadcasting (DAB), digital television, Wireless Local Area Network (WLAN), etc. Due to robustness against multipath fading, OFDM is expected to provide an efficient platform for high-speed data transmission.
An Orthogonal Frequency Division Multiple Access (OFDMA) system, which has recently attracted attention, is a multiple access system based on OFDM. It divides a frequency domain into subchannels each having a plurality of subcarriers and divides a time domain into a plurality of time slots. As time-frequency resources are allocated to users in units of subchannels, the OFDMA system can accommodate multiple users with limited frequency resources.
One of the international standardization organizations, the Institute of Electrical and Electronics Engineers (IEEE) 802.16 group has proposed IEEE 802.16e as a standard of providing a broadband wireless Internet service to Mobile Stations (MSs) in a Broadband Wireless Access (BWA) communication system such as the OFDMA system. The IEEE 802.16e standard enables transmission of more data for a shorter time due to a wider transmission bandwidth, compared to conventional wireless technologies aiming at voice service.
A mobile communication system for high-speed packet service such as the OFDMA system generally uses Automatic Repeat reQuest (ARQ) in which an MS notifies a Base Station (BS) of successful or failed reception of a packet transmitted from the BS in order to provide stable data transmission and the BS retransmits a failed packet to the MS. ARQ is one of several link control protocols, in which, when a received packet has errors, the MS requests retransmission of the packet to the BS.
To increase data rate and expand service coverage, a multi-hop technology is also under development for the high-speed packet data system. The multi-hop technology is a transmission technology that transmits data from a source node to a destination node via a Relay Station (RS) to thereby offer higher data rates and cover a large service area at a small cost.
The afore-mentioned IEEE 802.16 OFDMA standard is also under study in relation to the multi-hop technology. According to proposals made so far, ARQ is considered for reliable data transmission and reception in a Point-to-Multi-Point (PMP) environment between a Base Station (BS) and a Mobile Station (MS). However, there are no specified ARQ mechanisms and messages associated with a Relay Station (RS), in the case where the RS is added between the BS and the MS.
When an IEEE 802.16e-based multi-hop system is designed, consideration should be given to ARQ status management between the BS and the RS or between the RS and the MS. With no regard to the ARQ status management, data transmission and reception would be inefficient and retransmission of the same data would cause resource waste. Moreover, a delay involved in monitoring the status of the RS or the MS by the BS leads to an overall system delay.